Centralizing the Power Saving Mode for 802.11 Infrastructure Networks

With the rapid development of wireless networks, efficient energy management for wireless LAN (WLAN) has become an important problem, because mobile devices’ availability is determined by their stringent batteries power. Quite a few sources of energy consumption have been identified (Narseo et al., 2010), among which the wireless communication component uses up a significant amount of energy. For instance, the Motorola Droid phone consumes around 200mW with the backlight off, close to 400mW with the backlight on, and over 800mW when the Wi-Fi radio is active (Zeng et al., 2011). This chapter focuses on improving the energy efficiency of wireless communication component, because they may consume up to 50% of the total energy. Various mechanisms have been proposed to balance between communication quality and energy consumption for wireless devices, for example, power saving mode (PSM) that puts an idle client into a low-power mode (Gast, 2005), transmission power control (Nuggehalli et al., 2002), packet transmission scheduling (Qiao et al., 2003; Tarello et al., 2005), and some cross-layer methods (Anastasi et al., 2007). They investigate the trade-off between energy consumption and throughput (Gao et al., 2010; Zhang & Chanson, 2003), delay (Guha et al., 2010; Nuggehalli et al., 2002; 2006), or network utility (Chiang & Bell, 2004). In this chapter, we propose a centralized PSM (C-PSM), an AP-centric deployment of the IEEE 802.11 PSM, to optimize power saving and multiple performance metrics for infrastructure networks which are widely deployed in enterprise, campus, and metropolitan networks. In these networks, wireless clients (e.g., laptops, PDAs and mobile phones) using the IEEE 802.11 infrastructure mode connect to the Internet through an access point (AP). The experiment results show that significant improvements can be obtained from the new deployment of C-PSM. The IEEE 802.11 PSM, widely used in WLAN, allows an idle client to go into a sleep mode. Hereafter, we use PSM to refer to the IEEE 802.11 PSM. The clients save energy by sleeping while wakes up periodically to receive beacon frames from AP. The beacon frame, sent by an access point (AP) every beacon interval (BI), indicates whether clients have frames buffered at the AP. Each client’s wake-up frequency is determined by a PSM parameter listen interval (LI). Both BI and LI are configurable, and their settings directly influence the PSM’s performance shown by the analysis of section 4. Unfortunately, the protocol does not prescribe how the BI 1